chore: import upstream snapshot with attribution

server/functions/ln.go

@@ -0,0 +1,92 @@
+// Copyright 2024 Dolthub, Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either lnress or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package functions
+
+import (
+	"math"
+	"strings"
+
+	"github.com/cockroachdb/apd/v3"
+	"github.com/cockroachdb/errors"
+	"github.com/dolthub/go-mysql-server/sql"
+
+	"github.com/dolthub/doltgresql/server/functions/framework"
+	pgtypes "github.com/dolthub/doltgresql/server/types"
+)
+
+// initLn registers the functions to the catalog.
+func initLn() {
+	framework.RegisterFunction(ln_float64)
+	framework.RegisterFunction(ln_numeric)
+}
+
+// ln_float64 represents the PostgreSQL function of the same name, taking the same parameters.
+var ln_float64 = framework.Function1{
+	Name:       "ln",
+	Return:     pgtypes.Float64,
+	Parameters: [1]*pgtypes.DoltgresType{pgtypes.Float64},
+	Strict:     true,
+	Callable: func(ctx *sql.Context, _ [2]*pgtypes.DoltgresType, val1 any) (any, error) {
+		if val1.(float64) == 0 {
+			return nil, errors.Errorf("cannot take logarithm of zero")
+		} else if val1.(float64) < 0 {
+			return nil, errors.Errorf("cannot take logarithm of a negative number")
+		}
+		return math.Log(val1.(float64)), nil
+	},
+}
+
+// ln_numeric represents the PostgreSQL function of the same name, taking the same parameters.
+var ln_numeric = framework.Function1{
+	Name:       "ln",
+	Return:     pgtypes.Numeric,
+	Parameters: [1]*pgtypes.DoltgresType{pgtypes.Numeric},
+	Strict:     true,
+	Callable: func(ctx *sql.Context, _ [2]*pgtypes.DoltgresType, val1 any) (any, error) {
+		dec := val1.(*apd.Decimal)
+		if dec.Sign() == 0 {
+			return nil, errors.Errorf("cannot take logarithm of zero")
+		} else if dec.Sign() < 0 {
+			return nil, errors.Errorf("cannot take logarithm of a negative number")
+		} else if dec.Form == apd.NaN || dec.Form == apd.Infinite {
+			return dec, nil
+		}
+
+		// calculate precision and scale
+		exp := dec.Exponent
+		p := dec.NumDigits()
+		if exp < -16 {
+			p += int64(-exp)
+		} else {
+			p += 16
+		}
+
+		res := new(apd.Decimal)
+		_, err := sql.DecimalCtx.WithPrecision(uint32(p)).Ln(res, dec)
+		if err != nil {
+			return nil, err
+		}
+
+		// calculate exponent
+		if exp > -16 {
+			// use ln result
+			parts := strings.Split(res.Text('f'), ".")
+			whole := int32(len(parts[0]) / 2)
+			exp = whole - 16
+		}
+
+		return sql.DecimalRound(res, -exp)
+	},
+}